The present invention relates to a projecting apparatus having the function of automatic focus adjustment.
As well known, in patterning a wafer providing a substrate of semiconductor integrated circuits by the photoetching technique, a very high resolution is required and therefore a focus adjustment must be effected with high precision.
With the progress of the integrated circuitry technology, on the other hand, the pattern density has been so increased that the depth of focus is required not to exceed .+-.5 microns in tolerable error. Thus a problem is posed by the focus error of the projecting apparatus caused by the change of atmospheric temperature or the change of material with temperature.